Estimation of Pile Shaft Friction in Expansive Soil upon Water Infiltration

This study addresses the critical role of shaft friction of pile in the interaction with expansive soil under varying moisture content. A simplified estimation method is proposed, capturing the non-linear correlation between the interface relative displacement between the soil and pile and unit skin friction and during water infiltration. The approach integrates soil-pile displacement, interface shear strength parameters, and soil matric suction fluctuations. Tests on Nanyang expansive soil include a laboratory model with water infiltration, constant volume swelling, direct shear for interface shear strength, and a filter paper method for SWCC determination. Initial water content of 21% shows an increases swelling pressure more than 24% and 27%. Increasing soil water content reduces soil matric suction. Due to lower soil matric suction, cohesion, friction, and soil interface shear strength decreased. After the passage of the infiltration duration (specifically, 200 hours), ground heave peaks at 10.7 mm, potentially affecting pile axial forces. As matric suction diminishes, the pile’s shaft friction reduces, transferring more weight to the pile base, leading to settlements. Experimental data validate the proposed shaft friction estimation method. The approach aligns with previous studies and laboratory models, providing a comprehensive understanding of soil-pile interaction in changing moisture conditions.